Apparatus for determining the gas content of drilling muds

ABSTRACT

In the representative embodiment of the apparatus of the present invention disclosed herein, first and second selectively-movable pistons are respectively arranged within complementary first and second cylinders having their working chambers in fluid communication with one another to define an expansible sample chamber. Suitable control devices are provided to selectively extend the first piston for inducting a predetermined volume of drilling mud into the sample chamber and thereafter extend the second piston for reducing the pressure in the sample chamber to a predetermined reduced pressure which is preferably somewhat greater than the saturation pressures of any gases which might possibly be entrained in the entrapped mud sample. A suitable measuring device is cooperatively arranged for measuring the extension or displacement volume of the second piston for accurately determining the gas content of the entrapped sample.

United States Patent [1 1 11] 3,731,530 Tanguy et al. 1 May 8, 1973 [54]APPARATUS FOR DETERMINING THE [57] ABSTRACT GAS CONTENT OF DRILLING MUDS[75] Inventors: Denis R. Tanguy; Joseph F. Kishel,

both of Clarks Summit, Pa.

[73] Assignee: Schlumberger Technology Corporation, New York, NY.

[22] Filed: Mar. 20, 1972 [21] Appl. No.: 236,414

[52] U.S. Cl. ..73/l53, 73/61 R [51] Int. Cl. ..E2lb 49/00 [58] Field ofSearch ..73/l53, 19, 61 R; 23/230 HC, 232 R [56] References Cited UNITEDSTATES PATENTS 2,280,086 4/1942 Hayward ..l75/l83 2,799,561 7/1957Rochon ..73/l9 X 3,521,478 7/1970 Magorien ..73/i9 PrimaryExaminer-Jerry W. Myracle Attorney-Ernest R. Archambeau, Jr. et al.

87 86c c t 82 7g In the representative embodiment of the apparatus ofthe present invention disclosed herein, first and secondselectively-movable pistons are respectively arranged withincomplementary first and second cylinders having their working chambersin fluid communication with one another to define an expansible samplechamber. Suitable control devices are provided to selectively extend thefirst piston for inducting a predetermined volume of drilling mud intothe sample chamber and thereafter extend the second piston for reducingthe pressure in the sample chamber to a predetermined reduced pressurewhich is preferably somewhat greater than the saturation pressures ofany gases which might possibly be entrained in the entrapped mud sample.A suitable measuring device is cooperatively arranged for measuring theextension or displacement volume of the second piston for accuratelydetermining the gas content of the entrapped sample.

APPARATUS FOR DETERMINING THE GAS CONTENT OF DRILLING MUDS Those skilledin the art will, of course, appreciate that while drilling an oil or gaswell, a drilling control fluid or so-called mud" is customarilycirculated through the drill string and drill bit and then returned tothe surface by way of the annulus defined' between the walls of theborehole and the exterior of the drill string. In addition to coolingthe drill bit and transporting the formation cuttings removed thereby tothe surface, the mud. also functions to impose a positive pressure onthe earth formations penetrated by the drill bit. Thus, it is customaryto condition the drilling mud for maintaining its specific gravity orso-called mud weight at a selected level where the hydrostatic pressureof the column of mud in the borehole annulus will presumably besufficient to prevent or at least regulate the entry of high-pressureconnate fluids into the borehole from the formations penetrated by thedrill bit.

It is, however, not at all uncommon form the drill bit to unexpectedlypenetrate earth formations containing connate fluids at pressuresgreatly exceeding the hydrostatic head of the column of drilling mud atthat depth which will often result in either a so-called pressure kickor, even worse, a blowout. It will be appreciated that unless such ablowout is quickly checked, it may destroy the well and endanger livesand property at the surface. Thus, to be abundantly safe, it might beconsidered prudent to always maintain the density of the drilling mud atexcessively-high levels just to prevent such blowouts from occurring.Those skilled in the art will appreciate, however, that excessive muddensities will significantly impair drilling rates as well as quiteoften unnecessarily or irreparably damage potentially-producible earthformations. As a matter of expediency, therefore, it is preferred thatthe drilling mud be conditioned so as to maintain its density at a levelwhich is just sufficient to at least regulate, if not prevent, theunexpected entry of high-pressure formation gases into the borehole andinstead rely upon one or more of several typical measuring devices forhopefully detecting the presence of such gases in the returning drillingmud in time to take appropriate corrective actions.

Typical of these devices is the laboratory apparatus disclosed in U.S.Pat. No. 2,280,086 wherein a sample of drilling mud is drawn into aglass measuring tube and subjected to a reduced pressure to expand thesample for determining the amount of entrained gas. However, in additionto being unduly fragile, it is particularly difficult with thisapparatus either to precisely measure the sample volumes at the two testpressures or to accurately determine the reduced pressure during thefinal step. ltwill, of course, be appreciated that if either of thesemeasurements are imprecise, the resulting computation of the gas contentwill be correspondingly affected.

Other more-rugged test devices have also been proposed such as, forexample, those described in U.S. Pat. No. 2,138,141 and U.S. Pat. No.3,521,478. In the two devices shown in these patents, a single piston ismounted in a cylinder and cooperatively withdrawn for drawing aspecified volume of mud into the piston chamber. In the first patenteddevice, a gas measurement is purportedly obtained'by compressing thesample and measuring the initial and final pressures and volumes. Withthe second of these two patented devices, the piston is first withdrawnfurther for reducing the pressure in the piston chamber to a selectedvalue. The piston is then returned to compress the liberated gases toatmospheric pressure before determining the percentage of entrained gasin the mud sample. It will be appreciated, however, that in either testdevice, only a single piston is provided for hopefully obtaining aprecise volumetric measurement of the mud sample as well as for bringingthe pressure of the entrained gas to a precise final pressure. As aresult, the limited accuracy of these test devices simply precludesreliable measurements of small percentages of entrained gas,

Accordingly, it is an object of the present invention to provide a newand improved testing device for accurately determining the gas contentof drilling muds during the course of a typical drilling operation.

This and other objects of the present invention are attained byproviding means adapted for entrapping a precisely-measured volume of agas-bearing drilling mud in a sample chamber and including a firstcylinder in communication with the sample chamber and having a firstpiston member cooperatively arranged therein for selective movement toan extended position for precisely inducting a predetermined volume ofmud at a first pressure into the sample chamber; means adapted forprecisely reducing the pressure of a sample in the sample chamber andincluding a second cylinder in communication with the sample chamber andhaving a second piston member cooperatively arranged therein forselective movement to an extended position for precisely increasing thevolume of the sample chamber until the pressure of the mud sampletherein is reduced to a second predetermined pressure; and meansresponsive to the extension of the second piston for accuratelydetermining the increased chamber volume required to obtain this secondpressure to provide a precise measurement which is proportional to thegas content of the mud sample.

The novel features of the present invention are set forth withparticularity in the appended claims. The invention, together withfurther objects and advantages thereof, may be best understood by way ofthe following description of exemplary apparatus employing theprinciples of the invention as illustrated in the accompanying drawings,in which:

FIG. 1 schematically illustrates a portion of a typical rotary drillingrig and its associated mud-circulating system along with new andimproved gas-measuring apparatus of the present invention; and

FIG. 2 schematically depicts a preferred embodiment of a gas-measuringsystem arranged in accordance with the principles of the presentinvention.

Turning now to FIG. 1, a gas-measuring system 10 employing theprinciples of the present invention is schematically illustrated as itmay be employed in conjunction with a conventional rotary-drillingoperation in which a so-called drilling mud" is circulated. As-iscustomary, the drillingoperation is accomplished by means of a typicaldrilling rig 11 which is suitably arranged for drilling a borehole 12through various earth formations, as at 13, until a desired depth isattained.

The drilling rig l1 conventionally includes a drilling platform 14carrying a derrick 15 which supports typical cable-hoisting machinery(not shown) suitably arranged for supporting a swivel 16 and a tubularkelly 17. The drilling rig 11 further includes a rotary table 18operatively arranged on the rig floor 14 for rotatively driving thekelly 17 which supports a depending string 19 of drill pipe and drillcollars carrying a typical rotary drilling bit 20.

As is customary, the borehole 12 is filled with a supply of drilling mudfor maintaining pressure control of the various earth formations, as at13; and, as indicated by the several arrows seen in FIG. 1, the drillingmud is continuously circulated between the surface and the bottom of theborehole during the course of a drilling operation for cooling the drillbit 20 as well as for carrying away cuttings as they are removed by thedrill bit. To circulate the drilling mud, the drilling rig l 1 furtherincludes a mud-circulating system 21 which conventionally has ahigh-pressure circulating pump 22 coupled to the kelly 17 and the drillstring 19 by means of suitable piping 23 and a flexible hose 24connected to the swivel 16. The drilling mud is returned to the surfaceby way of a return line 25 coupled to the surface casing 26 typicallylining the uppermost portions of the borehole 12 and an open-top trough27 which is customarily arranged to discharge the returning drilling mudinto a so-called mud pit 28. A suction pipe 29in the other end of themud pit 28 is coupled to the pump 22 for withdrawing the drilling mudcontained therein. Accordingly, it will be appreciated that as the pump22 is operated, the drilling mud is continuously pumped downwardlythrough the kelly 17 and the drill string 19 and then discharged fromone or more ports in the drill bit 20 into the bottom of the borehole12. As the drilling mud leaves the drill bit 20, the cuttings beingremoved thereby will be carried in suspension by the column of viscousmud returning to the surface by way of the annulus space defined in theborehole 12 around the drill string 19.

It will, of course, be appreciated that should the drill bit 20 bepenetrating an earth formation, as at 13, containing high-pressure gas,there will be a corresponding increase in the gas content of thatportion of the drilling mud which is then exiting from the drill bit.Even though there may be a localized area of agitation around the bit20, experience has demonstrated that there is little or no intermixingof the several incremental portions of drilling mud constituting theoutgoing mud stream in the borehole 12. As a result, an increase in thegas content of a given portion of the returning drilling mud can beattributed to the presence of gas in the earth formation, as at 13,which was being penetrated by the drill bit 20 as that portion of mudleft the drill bit. Thus, by successively measuring the gas content ofincremental portions of the drilling mud entering the mud pit 28, usefulindications will be obtained of the nature of the earth formations, asat 13, being penetrated by the drill bit 20. If desired, the gas contentof the drilling mud entering the kelly 17 can also be determined toobtain a true differential measurement of the gas content of theoutflowing stream of drilling mud. It will, of course, be appreciatedthat in either situation, appropriate corrections must be made toaccount for the time required for a given increment of drilling mud tomove between the surface and the bottom of the borehole 12. Suchcorrections may, of course, be readily ascertained by those skilled inthe art.

Turning now to FIG. 2, the new and improved gasmeasuring system 10 ofthe present invention is depicted in a somewhat-schematic form. Ingeneral, the gas-measuring system 10 includes sample-inducting means 30cooperatively arranged for entrapping a precisely-measured sample ofpotentially gas-bearing drilling mud into an enclosed sample chamber 31,pressure-reducing means 32 adapted for precisely reducing the pressureof the entrapped mud sample to a predetermined lower pressure, andvolume-determining means 33 cooperatively arranged for providing aprecise measurement representative of the increased volume of theentrapped mud sample at the predetermined reduced pressure. Toselectively control the operation of the gas-measuring apparatus 10, agroup of controls, such as the automatic system shown generally at 34,is provided.

In the preferred embodiment of the present invention as illustrated inFIG. 2, the sample-inducting means 30 include an elongated cylinder 35defining an enclosed piston chamber 36 forming part of the samplechamber 31 and carrying a piston member 37 cooperatively arranged forreciprocating movement therein. To precisely delimit the longitudinalstroke or travel of the piston 37 within the cylinder 35, means areprovided such as a pair of longitudinally-spaced stop members 38 and 39which are cooperatively arranged at selected positions within the boreof the cylinder and on opposite sides of the piston. Accordingly, itwill be appreciated that since the internal bore of the cylinder 35 isof a uniform diameter and the locations of the fixed stops 38 and 39 areknown, the displacement volume of the sample-inducting means 30 isprecisely determined. Thus, by coupling a sample conduit, as at 40, tothe closed end of the piston chamber 36, movement of the piston 37 fromits illustrated full-line position to its extended position, as at 41,will be effective for drawing a precise volume of gas-bearing drillingmud into the sample chamber 31. Conversely, this entrapped volume ofdrilling mud will be displaced from the sample chamber 31 through themud conduit 40 whenever the piston 37 is returned from its extendedposition 41 to its initial position as illustrated in FIG. 2.

The pressure-reducing means 32 are similarly comprised of an elongatedcylinder 42 having a piston chamber 43 which is also cooperativelyarranged to be another portion of the sample chamber 31 and carries areciprocating piston member 44. To complete the sample chamber 31, aconduit 45 of suitable size is coupled between the cylinders 35 and 42in communication with the two piston chambers 36 and 43. Another conduit46 is coupled to the cylinder 42 to provide communication with thechamber 43.

The measuring system 10 further includes piston-actuating means such ashydraulic or pneumatic actuators 47 and 48 which are respectivelycoupled by connecting rods 49 and 50 to the pistons 37 and 44. As istypical, the actuator 47 is comprised of an elongated cylinder 51carrying an actuating piston 52 which is coupled to the connecting rod49 and cooperatively arranged for movement back and forth in response tothe operated control valves, such as normally-closed solenoid valves 55and 56 having one or more individual solenoid actuators as at 57 and 58,which are respectively coupled to the conduits 40 and 46 for selectivelycontrolling the entrance of drilling mud into the sample chamber 31 aswell as the release of liberated gas therefrom. The control system 34 isalso cooperatively arranged for selectively moving the pistons 37 and 44back and forth within their respective cylinders 35 and 42.

In the preferred embodiment of the gas-measuring system 10, thepressure-responsive actuator 47 is selectively controlled by couplingthe outlets of selectivelyoperated control valves, such as a pair ofthree-way solenoid valves 59 and 60, to opposite ends of the actuatorcylinder 51 by fluid lines 61 and 62 and coupling pressure supply lines63 and 64 between the inlet of these valves and a suitable source of apressured fluid (not shown) such as a conventional hydraulic orcompressed-air system. As is typical, the three-way valves 59 and 60 arearranged so that when their respective solenoid actuators 65 and 66 arenot energized, the 30 outlet conduits 61 and 62 will either berespectively vented, as at 67 and 68, to atmosphere where a pneumaticsystem is employed or else be returned to a reservoir' where a hydraulicsystem is employed. This arrangement will, of course, require that thesolenoid valves 59 and 60 be opened by energizing their respectivesolenoids 65 and 66 when it is desired to move the actuating piston 52to a different position.

Three-way solenoid valves 69 and 70 respectively having solenoidactuators 71 and 72 are similarly arranged for selectively controllingthe movements of the actuator piston 54. Hereagain, the inlets of thevalves 69 and 70 are coupled to pressure supply lines 71 and 72 and theoutlets of these valves are respectively connected by conduits 73 and 74to the opposite ends of the actuating cylinder 53. Pneumatic vent linesor hydraulic return lines 75 and 76 are respectively coupled to thesolenoid valves 69 and 70 in the same manner as previously describedwith respect to the 50 piston actuator 47.

The control system 34 is, of course, cooperatively arranged forselectively operating the several actuator control valves 59, 60, 69 and70 as well as the sample chamber control valves 55 and 56. Those skilledin the art will, of course, appreciate that many different arrangementsof timers, relays, sequence controls, limit switches and various typesof switches can be arranged to provide the control functions necessaryfor operating the measuring system 10. Thus, since the present inventionis not limited to any particular arrangement of controls, the controlsystem 34 is schematically depicted including a multi-position rotaryswitch 77,that is cooperatively arranged for providing the controlfunctions which, as will subsequently be explained, are essential to theoperation of the measuring system 10. As illustrated, the switch 77 isarranged to selectively supply power to the several solenoids 57, 58,65, 66, 71 and 72 at different times as respectively indicated by theletters A, B and C. To appreciate the effects of opening the severalsolenoid valves 59, 60, 69 and 70, the same identification characters A,B and C are also used to designate when the motivating fluid (i.e.,compressed air or hydraulic fluid) is admitted through a particularvalve to the actuators 47 and 48.

In the operation of the new and improved gas-measuring system 10 of thepresent invention, a mud sample is first drawn into the sample chamber31 by open ing the sample valve 55 and moving the piston 37 from itsfull-line position as depicted in FIG. 2 to its fully-extended positionas at 41. The sample valve 55 is reclosed to close off the entrapped mudsample in the sample chamber 31. Thereafter, the piston 44 is moved fromits full-line position toward an extended position, as at 78, forreducing the pressure in the sample chamber 31 to a predetermined valuewhich is known to be higher than the saturation pressure or flashingpressure of the liquid phase of the entrapped mud sample. These threesteps are essential for achieving the objects of the present invention;and it will, therefore, be appreciated that the control system 34 can bearranged in various manners to accomplish these objects withoutdeparting from the scope of the invention.

To understand the principles-of the present invention, it must berecognized that the physical characteristics of the mud sample entrappedin the sample chamber 31 will determine the distance which the piston 44must be moved outwardly to reduce the pressure in the sample chamber tothe aforementioned predetermined value. First of all, those skilled inthe art will appreciate that if only a gas instead of a gas-bearin gliquid was entrapped in the sample chamber 31, outward travel of thepiston member 44 from its fullyretracted position shown in FIG. 2 to anextended position, such as depicted at 78, would simply expand the gasin direct relation to the distance traveled by the pressure-reducingpiston. Thus, in this unlikely situation, outward travel of the piston44 will simply reduce the pressure of the entrapped gas sample inkeeping with the general gas laws.

The situation just described will, of course, be significantly differentwhere an entirely-liquid sample is entrapped in the sample chamber 31.Assuming that the actuator 48 is incapable of pulling the piston 44outwardly with sufficient force to reduce the pressure of the entrappedliquid sample to or below its saturation pressure and thereby induceflashing of the liquid sample, it will be appreciated that there will beno perceptible movement of the piston 44 away from its fullyretractedposition illustrated in FIG. 2 before the pressure in the sample chamber31 is reduced to the aforementioned predetermined value.

In the usual situation, however, there will generally be at least aminor quantity of gas entrained or dis- 0 solved in a given mud sampletrapped in the sample chamber 31. It has been found that the percentageof gas contained in such a gas-bearing sample can be computed by thefollowing equation:

g s=[( 2/( r 2)]( 1) where,

P, initial pressure of mud sample, psia P final reduced pressure of mudsample, psia A area of piston member 44, sq. in.

V volume of mud sample, cu. in.

X distance piston member 44 extended to reach final pressure P in.

Accordingly, in the operation of the gas-measuring apparatus 10, theseveral movable elements of the apparatus are initially positioned asillustrated in FIG. 2. For reasons that will subsequently be explained,it is preferred that the sample chamber 31 (i.e., the piston chambers 36and 43 as well as the interconnecting conduit 45) be initially filledwith water. Thereafter, with the control system 34, movement of therotary switch 77 to the A position will simultaneously apply power tothe solenoids 57 and 65 to open the actuator 59 for effecting outwardmovement of the sample-induction piston 52 as well as to open the samplevalve 55 for allowing a sample of drilling mud to be inducted into thesample chamber 31 as the sample-inducting piston is moved outwardly toits extended position as at 41. The power could just as well be appliedsuccessively to the solenoids 57 and 65 so long as a sample of drillingmud is pulled into the chamber 31.

It will be appreciated, therefore, that since the volume of waterinitially trapped between the closed valves 55 and 56 and in front ofthe pistons 37 and 44 when they are in their fully-retracted positionsis precisely known, movement of the sample-inducting piston to itsoutward position 41 will induct a preciselydetermined volume of thedrilling mud into the sample chamber 31. Thus, once the piston 37 hasreached its outward position 41, the volume, V of the mud sample will beaccurately established to permit precise determination of the gascontent therein by means of Equation 1.

Once the sample-inducting piston 37 has reached its extended position41, the rotary switch 77 is advanced to the switch position B. Asillustrated in FIG. 2, the actuator valve 59 is left open to insure thatthe sample-inducting piston remains in its fully-extended position. Withthe control system 34, the advancement of the switch 77 will alsosimultaneously apply electrical power to the solenoid 71 for opening theactuator valve 69 to admit the pressured motivating fluid into thelefthand end of the actuator cylinder 53 for carrying the piston 44outwardly toward, for example, the extended position indicated by 78. Itwill, of course, be appreciated that the actuator valve 69 could also beopened by means of a limit switch (not shown) which would be arranged torespond to movement of the sample-inducting piston 37 to its position at39.

As previously described, however, outward movement of thepressure-reducing piston 44 is continued only until such time that thepressure in the sample chamber 31 is reduced to a predetermined minimum.Thus, in the preferred manner of accomplishing this, apressure-responsive switch 79 is cooperatively arranged for sensing thepressure in the sample chamber 31 and cutting the electrical powersupplied to the solenoid 71 for reclosing the valve 69 once the pressurein the sample chamber has reached this predetermined minimum. This will,of course, halt the pressure-reducing piston 44 so that a typicalposition transducer 80 coupled thereto will provide an immediatereading, as on a recorder 81, which is indicative of the outwarddisplacement, X, of the pressure-reducing piston. Thus,

since all of the several factors in Equation l except for thedisplacement distance, X, are predetermined constants, once the recorder81 has recorded either the extent of the displacement of thepressure-reducing piston 44 or a function thereof, the gas content ofthe sample of drilling mud will be precisely determined. Thereafter, therotary switch 77 is advanced to the position C for returning the pistons37 and 44 to their respective retracted positions as well as opening thevalves 55 and 56 to discharge the mud sample back through the conduitand into the mud trough 27 as well as to purge the sample chamber 31 ofcollected gas as at 82.

It will be appreciated that by leaving the valves 55 and 56 open, freshwater, as at 83, can be introduced into the sample chamber 31 forwashing out any residual traces of the drilling mud or cuttings whichwould otherwise tend to accumulate in the sample chamber andprogressively decrease the volume of the sample chamber and therebyimpair the accuracy of the measurements. In the preferred embodiment ofthe gas-measuring apparatus 10, fresh water is admitted to the samplechamber 31 and gas is purged therefrom by means of an invertedgas-collection chamber 84 which is coupled to the inlet of the valve 56.Since the gas-collection chamber 84 will ordinarily be filled withwater, a float-operated valve, as schematically depicted at 85, iscooperatively arranged for preventing water from entering a gas outletconduit 86 on top of the collection chamber and coupled to typicalgas-analysis device 87.

Accordingly, once gas is purged from the sample chamber 31 by returningthe pistons 37 and 44 to their retracted positions, the gas will becollected in the upper portion of the collection chamber 84 and therebycause the float-operated valve 85 to open. Once the valve 85 opens, thecollected gas will be displaced from the chamber 84 by the waterentering the bottom of the collection chamber and dispatched through theoutlet conduit 86 to the gas-analysis device 87. The valve 85 will, ofcourse, reclose once the water refills the collection chamber 84.

As previously mentioned, so long as the valves 55 and 56 remain open,water will be flushed through the sample chamber 31 to assure there isno debris or residue left in the sample chamber. Thus, until the rotaryswitch 77 is advanced from its C position to its initial startingposition, this flushing action will continue. This can, of course, beaccomplished either by a controlled sequence or by selection.

Accordingly, it will be appreciated that the present invention hasprovided new and improved testing apparatus for accurately determiningeven minute quantities of entrained or dissolved gases in typicalborehole drilling muds. By arranging the new and improved test ingapparatus of the present invention to include first and second pistonsand cylinders which are cooperatively coupled together to define acommon sample chamber, the first piston and cylinder can be selectivelysized for inducting a precise quantity of drilling mud into the samplechamber and the second piston and cylinder can be selectively sized forexpanding the total volume of the sample chamber as required to reducethe pressure of the mud sample to a predetermined reduced value. Thus,in clear contrast to the prior-art testing devices, the measuringapparatus of the present invention is cooperatively arranged in a uniquefashion both to collect a precise volume of drilling mud and to reducethe pressure of this mud sample to a precise predetermined pressure.

While only a particular embodiment of the present invention has beenshown and described, it is apparent that changes and modifications maybe made without departing from this invention in its broader aspects;and, therefore, the aim in the appended claims is to cover all suchchanges and modifications as fall within the true spirit and scope ofthis invention.

What is claimed is:

1. Apparatus adapted for determining the gas content of a drilling mudand comprising:

means defining a sample chamber;

first means adapted for inducting drilling mud into said sample chamberand including a first piston cylinder in communication with said samplechamber, a first piston cooperatively arranged in said first cylinderand adapted for movement therein from a predetermined retracted positionto a predetermined extended position, and first actuating means coupledto said first piston and adapted for selectively moving said firstpiston from its said retracted position to its said extended position toinduct a predetermined volume of drilling mud into said sample chambercorresponding to the displacement volume defined in said first cylinderbetween said predetermined positions of said first piston;

second means adapted for reducing the pressure of a sample of drillingmud inducted into said sample chamber and including a second pistoncylinder in communication with said sample chamber, a second pistoncooperatively arranged in said second cylinder and adapted for movementtherein from a retracted position to extended posi tions, and secondactuating means coupled to said second piston and adapted forselectively moving said second piston away from its said retractedposition to reduce the pressure of a sample of drilling mud in saidsample chamber in accordance with the gas content of a sample ofdrilling mud in said sample chamber and the increased volume therein assaid second piston is moved away from its said retracted position;

pressure-responsive means adapted for determining when the pressure of asample of drilling mud in said sample chamber is reduced to apredetermined value in response to movement of said second piston awayfrom its said retracted position;and

third means operable upon movement of said second piston away from itssaid retracted position for determining the increase in the volume ofsaid sample chamber upon movement of said second piston to an extendedposition where the pressure ofa sample of drilling mud in said samplechamber is reduced to said predetermined value.

2. The apparatus of claim 1 wherein said pressure responsive meansinclude means operatively associated with said second actuating meansand adapted for discontinuing operation of said second actuating meanswhenever the pressure of a sample of drilling mud in said sample chamberis reduced to said predetermined value.

3. The apparatus of claim 2 wherein said third means include meansoperatively associated with said second actuating means and adapted forproviding an indication representative of the distance between saidretracted position of said second piston and said extended positionthereof whenever the operation of said second actuating means isdiscontinued.

4. The apparatus of claim 1 wherein said third means include meansoperatively associated with said second actuating means and adapted forproviding an indication representative of the distance between saidretracted position of said second piston and said extended positionthereof when the pressure in said sample chamber is reduced to saidpredetermined value.

5. The apparatus of claim 1 further including means selectively operablefor introducing a flushing agent into said sample chamber and said firstand second cylinders after a sample of drilling mud has been dischargedtherefrom.

6. The apparatus of claim 1 further including gasreceiving means incommunication with said sample chamber and adapted for receiving gascontained in a sample of drilling mud in said sample chamber after sucha sample has been discharged therefrom.

7. The apparatus of claim 1 further including control means operativelyassociated with said first and second means and adapted for sequentiallyoperating said first actuating means to move said first piston to itssaid extended position and thereafter operating said second actuatingmeans to move said second piston away from its said retracted position.

8. Apparatus adapted for determining the gas content of a drilling mudand comprising:

means defining a sample chamber and first and second piston chambers influid communication therewith;

first means adapted for inducting a predetermined volume of drilling mudinto said sample chamber and including a mud conduit in communicationwith said sample chamber, a mud-control valve in said mud conduit andoperatively arranged to be opened and closed for controlling the flow ofdrilling mud between said sample chamber and a source of drilling mud tobe tested, a first piston cooperatively arranged in said first cylinderand adapted for movement therein between predetermined retracted andextended positions, and first actuating means coupled to said firstpiston and adapted for selectively moving said first piston from itssaid retracted position to its said extended position to induct apredetermined volume of drilling mud into said sample chambercorresponding to the displacement volume defined in said first cylinderbetween said predetermined positions of said first piston;

second means adapted for reducing the pressure of a sample of drillingmud inducted into said sample chamber and including a second pistoncooperatively arranged in said second cylinder and adapted for movementtherein between retracted and extended positions, and second actuatingmeans coupled to said second piston and adapted for selectively movingsaid second piston away from its said retracted position to reduce thepressure of a sample of drilling mud in said sample chamber inaccordance with the gas content of a sample of drilling mud in saidsample chamber and the increased volume therein as said second piston ismoved away from its said retracted position pressure-responsive meansadapted for providing a control signal whenever the pressure of a sampleof drilling mud in said sample chamber is reduced to a predeterminedvalue in response to movement of said second piston away from its saidretracted position; indicating means operable upon movement of saidsecond piston away from its said retracted position for indicating thevolumetric increase of said sample chamber upon movement of said secondpiston to an extended position where the pressure in said sample chamberis reduced to said predetermined value; and

control means operatively associated with said actuating means and saidpressure-responsive means and adapted for operating said first actuatingmeans to move said first piston from its said retracted position to itssaid extended position for inducting said predetermined volume ofdrilling mud into said sample chamber and thereafter operating saidsecond actuating means to move said second piston from its saidretracted position until said pressure-responsive means provides saidcontrol signal.

9. The apparatus of claim 8 wherein said indicating means include meansresponsive to movement of said second piston for providing an outputsignal representative of the distance said second piston is moved awayfrom its said retracted position for determining the volume increase insaid sample chamber required to reduce the pressure therein to saidpredetermined value.

10. The apparatus of claim 9 further including recording meansoperatively associated with said indicating means and adapted forrecording said output signal.

11. The apparatus of claim 8 wherein said control means further includevalve-actuating means operatively associated with said mud-control valveand adapted for opening said mud-control valve at least before saidfirst actuating means move said first piston away from its saidretracted position and closing said mud-control valve after said firstpiston reaches its said extended position and at least before saidsecond actuating means move said second piston away from its saidretracted position.

12. The apparatus of claim 8 further including a fluid conduit incommunication with said sample chamber, a conduitcontrol valve in saidfluid conduit and operatively arranged to be opened and closed forcontrolling the flow of fluid through said fluid conduit, and meanscoupled to said fluid conduit and adapted for introducing a flushingfluid into said sample chamber and said first and second cylinders aftera sample of drilling mud has been discharged therefrom upon opening ofsaid valves.

13. The apparatus of claim 8 further including a fluid conduit incommunication with said sample chamber, a conduit-control valve in saidfluid conduit and operatively arranged to be opened and closed forcontrolling the flow of fluid through said fluid conduit, and meanscoupled to said fluid conduit and adapted for receiving gas contained ina sample of drilling mud in said sample chamber after said pistons havebeen moved to their respective said extended positions and at leastafter said conduit-control valve is openedv 14. Apparatus adapted fordetermining the gas content of a drilling mud and comprising:

means defining a sample chamber having upper and lower fluid openings;first means adapted for inducting a predetermined volume of drilling mudinto said sample chamber and including a mud conduit coupled to saidlower opening, a mud-control valve in said mud conduit, firstvalve-actuating means coupled to said mudcontrol valve and adapted foropening and closing said mud-control valve to control the flow ofdrilling mud between said sample chamber and a source of drilling mud tobe tested, a first piston cylinder in communication with said samplechamber, a first piston cooperatively arranged in said first cylinderand adapted for movement therein from a predetermined retracted positionto a predetermined extended position, and first piston-actuating meanscoupled to said first piston and adapted for selectively moving saidfirst piston from its said retracted position to its said extendedposition to induct a predetermined volume of drilling mud into saidsample chamber corresponding to the displacement volume defined in saidfirst cylinder between said predetermined positions of said firstpiston; second means adapted for reducing the pressure of a sample ofdrilling mud inducted into said sample chamber and including a fluidconduit coupled to said upper opening, a fluid-control valve in saidfluid conduit, second valve-actuating means coupled to saidfluid-control valve and adapted for opening and closing saidfluid-control valve to control the flow of fluids through said fluidconduit, a second piston cylinder in communication with said samplechamber, a second piston cooperatively arranged in said second cylinderand adapted for movement therein from a retracted position to extendedpositions, and second pistonactuating means coupled to said secondpiston and adapted for selectively moving said second piston away fromits said retracted position to reduce the pressure ofa sample ofdrilling mud in said sample chamber in accordance with the gas contentof a sample of drilling mud in said sample chamber and the increasedvolume therein as said second piston is moved away from its saidretracted position; pressure-responsive means in communication with saidsample chamber and adapted for producing an output signal when thepressure of a sample of drilling mud in said sample chamber is reducedto a predetermined value in response to movement of said second pistonaway from its said retracted position; control means cooperativelyassociated with said actuating means and said pressure-responsive meansand adapted for sequentially operating said first and secondvalve-actuating means and said first piston-actuating means to open saidmud-control valve, close said fluid-control valve and enable said firstpiston-actuating means to move said first piston from its said retractedposition to its said extended position for inducting said predeterminedvolume of drilling mud through said mud conduit into said sample chamberand thereafter operating said first valve-actuating means and saidsecond pistonactuating means to close said mud-control valve and enablesaid second piston-actuating means to move said second piston from itssaid retracted position until said second piston-actuating means halt inresponse to said output signal to stop said second piston at one of itsextended positions; and

indicating means cooperatively associated with said secondpiston-actuating means for providing an indication representative of theincreased volume of said sample chamber required to reduce the pressureof a sample of drilling mud in said sample chamber to said predeterminedvalue.

15. The apparatus of claim 14 wherein said indicating means includemeans responsive to movement of said second piston for providing anoutput signal representative of the distance said second piston is movedaway from its said retracted position for determining the volumeincrease in said sample chamber required to reduce the pressure thereinto said predetermined value.

16. The apparatus of claim 15 further including recording meansoperatively associated with said indicating means and adapted forrecording said output signal.

17. The apparatus of claim 14 wherein said control means further includemeans operable after said second piston-actuating means halt foroperating said actuating means to return said pistons to their saidretracted positions and open said control valves for displacing drillingmud from said sample chamber through said mud conduit and displacing gasfrom said sample chamber through said fluid conduit.

18. The apparatus of claim 17 further including gascollection means incommunication with said fluid conduit and adapted for receiving gasdisplaced from said sample chamber upon return of said pistons to theirsaid retracted positions.

19. The apparatus of claim 17 further including chamber-flushing meansin communication with said fluid conduit and adapted for discharging aflushing agent through said sample chamber upon return of said pistonsto their said retracted positions.

20. The apparatus of claim 19 further including gascollection means incommunication with said fluid conduit and adapted for receiving gasdisplaced from said sample chamber upon return of said pistons to theirsaid retracted positions.

1. Apparatus adapted for determining the gas content of a drilling mudand comprising: means defining a sample chamber; first means adapted forinducting drilling mud into said sample chamber and including a firstpiston cylinder in communication with said sample chamber, a firstpiston cooperatively arranged in said first cylinder and adapted formovement therein from a predetermined retracted position to apredetermined extended position, and first actuating means coupled tosaid first piston and adapted for selectively moving said first pistonfrom its said retracted position to its said extended position to inducta predetermined volume of drilling mud into said sample chambercorresponding to the displacement volume defined in said first cylinderbetween said predetermined positions of said first piston; second meansadapted for reducing the pressure of a sample of drilling mud inductedinto said sample chamber and including a second piston cylinder incommunication with said sample chamber, a second piston cooperativelyarranged in said second cylinder and adapted for movement therein from aretracted position to extended positions, and second actuating meanscoupled to said second piston and adapted for selectively moving saidsecond piston away from its said retracted position to reduce thepressure of a sample of drilling mud in said sample chamber inaccordance with the gas content of a sample of drilling mud in saidsample chamber and the increased volume therein as said second piston ismoved away from its said retracted position; pressure-responsive meansadapted for determining when the pressure of a sample of drilling mud insaid sample chamber is reduced to a predetermined value in response tomovement of said second piston away from its said retracted position;and third means operable upon movement of said second piston away fromits said retracted position for determining the increase in the volumeof said sample chamber upon movement of said second piston to anextended position where the pressure of a sample of drilling mud in saidsample chamber is reduced to said predetermined value.
 2. The apparatusof claim 1 wherein said pressure-responsive means include meansoperatively associated with said second actuating means and adapted fordiscontinuing operation of said second actuating means whenever thepressure of a sample of drilling mud in said sample chamber is reducedto said predetermined value.
 3. The apparatus of claim 2 wherein saidthird means include means operatively associated with said secondactuating means and adapted for providing an indication representativeof the distance between said retractEd position of said second pistonand said extended position thereof whenever the operation of said secondactuating means is discontinued.
 4. The apparatus of claim 1 whereinsaid third means include means operatively associated with said secondactuating means and adapted for providing an indication representativeof the distance between said retracted position of said second pistonand said extended position thereof when the pressure in said samplechamber is reduced to said predetermined value.
 5. The apparatus ofclaim 1 further including means selectively operable for introducing aflushing agent into said sample chamber and said first and secondcylinders after a sample of drilling mud has been discharged therefrom.6. The apparatus of claim 1 further including gas-receiving means incommunication with said sample chamber and adapted for receiving gascontained in a sample of drilling mud in said sample chamber after sucha sample has been discharged therefrom.
 7. The apparatus of claim 1further including control means operatively associated with said firstand second means and adapted for sequentially operating said firstactuating means to move said first piston to its said extended positionand thereafter operating said second actuating means to move said secondpiston away from its said retracted position.
 8. Apparatus adapted fordetermining the gas content of a drilling mud and comprising: meansdefining a sample chamber and first and second piston chambers in fluidcommunication therewith; first means adapted for inducting apredetermined volume of drilling mud into said sample chamber andincluding a mud conduit in communication with said sample chamber, amud-control valve in said mud conduit and operatively arranged to beopened and closed for controlling the flow of drilling mud between saidsample chamber and a source of drilling mud to be tested, a first pistoncooperatively arranged in said first cylinder and adapted for movementtherein between predetermined retracted and extended positions, andfirst actuating means coupled to said first piston and adapted forselectively moving said first piston from its said retracted position toits said extended position to induct a predetermined volume of drillingmud into said sample chamber corresponding to the displacement volumedefined in said first cylinder between said predetermined positions ofsaid first piston; second means adapted for reducing the pressure of asample of drilling mud inducted into said sample chamber and including asecond piston cooperatively arranged in said second cylinder and adaptedfor movement therein between retracted and extended positions, andsecond actuating means coupled to said second piston and adapted forselectively moving said second piston away from its said retractedposition to reduce the pressure of a sample of drilling mud in saidsample chamber in accordance with the gas content of a sample ofdrilling mud in said sample chamber and the increased volume therein assaid second piston is moved away from its said retracted position;pressure-responsive means adapted for providing a control signalwhenever the pressure of a sample of drilling mud in said sample chamberis reduced to a predetermined value in response to movement of saidsecond piston away from its said retracted position; indicating meansoperable upon movement of said second piston away from its saidretracted position for indicating the volumetric increase of said samplechamber upon movement of said second piston to an extended positionwhere the pressure in said sample chamber is reduced to saidpredetermined value; and control means operatively associated with saidactuating means and said pressure-responsive means and adapted foroperating said first actuating means to move said first piston from itssaid retracted position to its said extended position for inducting saidpredetermined volume of drilling mud into said sample chamber andthereafter opErating said second actuating means to move said secondpiston from its said retracted position until said pressure-responsivemeans provides said control signal.
 9. The apparatus of claim 8 whereinsaid indicating means include means responsive to movement of saidsecond piston for providing an output signal representative of thedistance said second piston is moved away from its said retractedposition for determining the volume increase in said sample chamberrequired to reduce the pressure therein to said predetermined value. 10.The apparatus of claim 9 further including recording means operativelyassociated with said indicating means and adapted for recording saidoutput signal.
 11. The apparatus of claim 8 wherein said control meansfurther include valve-actuating means operatively associated with saidmud-control valve and adapted for opening said mud-control valve atleast before said first actuating means move said first piston away fromits said retracted position and closing said mud-control valve aftersaid first piston reaches its said extended position and at least beforesaid second actuating means move said second piston away from its saidretracted position.
 12. The apparatus of claim 8 further including afluid conduit in communication with said sample chamber, aconduit-control valve in said fluid conduit and operatively arranged tobe opened and closed for controlling the flow of fluid through saidfluid conduit, and means coupled to said fluid conduit and adapted forintroducing a flushing fluid into said sample chamber and said first andsecond cylinders after a sample of drilling mud has been dischargedtherefrom upon opening of said valves.
 13. The apparatus of claim 8further including a fluid conduit in communication with said samplechamber, a conduit-control valve in said fluid conduit and operativelyarranged to be opened and closed for controlling the flow of fluidthrough said fluid conduit, and means coupled to said fluid conduit andadapted for receiving gas contained in a sample of drilling mud in saidsample chamber after said pistons have been moved to their respectivesaid extended positions and at least after said conduit-control valve isopened.
 14. Apparatus adapted for determining the gas content of adrilling mud and comprising: means defining a sample chamber havingupper and lower fluid openings; first means adapted for inducting apredetermined volume of drilling mud into said sample chamber andincluding a mud conduit coupled to said lower opening, a mud-controlvalve in said mud conduit, first valve-actuating means coupled to saidmud-control valve and adapted for opening and closing said mud-controlvalve to control the flow of drilling mud between said sample chamberand a source of drilling mud to be tested, a first piston cylinder incommunication with said sample chamber, a first piston cooperativelyarranged in said first cylinder and adapted for movement therein from apredetermined retracted position to a predetermined extended position,and first piston-actuating means coupled to said first piston andadapted for selectively moving said first piston from its said retractedposition to its said extended position to induct a predetermined volumeof drilling mud into said sample chamber corresponding to thedisplacement volume defined in said first cylinder between saidpredetermined positions of said first piston; second means adapted forreducing the pressure of a sample of drilling mud inducted into saidsample chamber and including a fluid conduit coupled to said upperopening, a fluid-control valve in said fluid conduit, secondvalve-actuating means coupled to said fluid-control valve and adaptedfor opening and closing said fluid-control valve to control the flow offluids through said fluid conduit, a second piston cylinder incommunication with said sample chamber, a second piston cooperativelyarranged in said second cylinder and adapted for movement therein from aretracted posiTion to extended positions, and second piston-actuatingmeans coupled to said second piston and adapted for selectively movingsaid second piston away from its said retracted position to reduce thepressure of a sample of drilling mud in said sample chamber inaccordance with the gas content of a sample of drilling mud in saidsample chamber and the increased volume therein as said second piston ismoved away from its said retracted position; pressure-responsive meansin communication with said sample chamber and adapted for producing anoutput signal when the pressure of a sample of drilling mud in saidsample chamber is reduced to a predetermined value in response tomovement of said second piston away from its said retracted position;control means cooperatively associated with said actuating means andsaid pressure-responsive means and adapted for sequentially operatingsaid first and second valve-actuating means and said firstpiston-actuating means to open said mud-control valve, close saidfluid-control valve and enable said first piston-actuating means to movesaid first piston from its said retracted position to its said extendedposition for inducting said predetermined volume of drilling mud throughsaid mud conduit into said sample chamber and thereafter operating saidfirst valve-actuating means and said second piston- actuating means toclose said mud-control valve and enable said second piston-actuatingmeans to move said second piston from its said retracted position untilsaid second piston-actuating means halt in response to said outputsignal to stop said second piston at one of its extended positions; andindicating means cooperatively associated with said secondpiston-actuating means for providing an indication representative of theincreased volume of said sample chamber required to reduce the pressureof a sample of drilling mud in said sample chamber to said predeterminedvalue.
 15. The apparatus of claim 14 wherein said indicating meansinclude means responsive to movement of said second piston for providingan output signal representative of the distance said second piston ismoved away from its said retracted position for determining the volumeincrease in said sample chamber required to reduce the pressure thereinto said predetermined value.
 16. The apparatus of claim 15 furtherincluding recording means operatively associated with said indicatingmeans and adapted for recording said output signal.
 17. The apparatus ofclaim 14 wherein said control means further include means operable aftersaid second piston-actuating means halt for operating said actuatingmeans to return said pistons to their said retracted positions and opensaid control valves for displacing drilling mud from said sample chamberthrough said mud conduit and displacing gas from said sample chamberthrough said fluid conduit.
 18. The apparatus of claim 17 furtherincluding gas-collection means in communication with said fluid conduitand adapted for receiving gas displaced from said sample chamber uponreturn of said pistons to their said retracted positions.
 19. Theapparatus of claim 17 further including chamber-flushing means incommunication with said fluid conduit and adapted for discharging aflushing agent through said sample chamber upon return of said pistonsto their said retracted positions.
 20. The apparatus of claim 19 furtherincluding gas-collection means in communication with said fluid conduitand adapted for receiving gas displaced from said sample chamber uponreturn of said pistons to their said retracted positions.